Directional boring, often called horizontal directional drilling (HDD), is in common use for installation of pipelines, cables and culverts. Such operations are often undertaken in environmentally sensitive places such as under rivers and near residential areas. The need for biodegradable, low toxicity fluids for use in oil and gas drilling operations has been recognized, as in U.S. Pat. No. 7,392,844. Such drilling fluids are made of organic chemicals: liquids, polymers and the like suited for down hole drilling. Drilling fluids for directional drilling are entirely different and not comparable to those used in down hole drilling. HDD fluid is used to lubricate a drill bit by ejection from orifices in the bit, and in some machines is used to power the drill, i.e. a so called mud motor drill. The mud once ejected from the bit flows into the borehole being formed, usually flowing rearwardly to the open end of the hole. At this location suction is used in an attempt to recover as much of the drilling fluid as possible for re-use.
Since directional drilling fluid is used on or near the earth's surface some degree of release into the environment is unavoidable, and the area over which release can occur can vary greatly. Directional drilling fluid is commonly an aqueous suspension of bentonite (clay) which is non-toxic and inert. However, bentonite based drilling fluids are inorganic and hence not biodegradable, and therefore can have undesirable effects on the environment. For example, after a directional drilling run using conventional drilling fluid, a pool of thick sludge forms at the exit and/or entry site. If not cleaned up or recycled, it solidifies into a hard, clay material.
Other, more difficult to deal with forms of leakage commonly occur. If cracks develop in the side of the drill bore during drilling, then drilling fluid can be pumped up to the ground's surface. Loss of drilling fluid at a location other than the beginning or end of the bore is referred to in the well drilling and horizontal directional drilling arts as “fracking out”. In a bore being drilled under a river that is a salmon stream, the bentonite leaks into the river bed and contaminates fish eggs laid there. Although it is non-toxic, it is still capable of harming a fragile ecosystem such as a trout stream. Thus, there is a strong need for a drilling fluid composition that is biodegradable, and also can provide a way of stopping seepage when fracking out occurs. Indeed in very loose soil such as cobble the rate of fluid loss can be so great that recycling of the drilling fluid is not possible. A drilling fluid is needed that can be used in loose soil formations without excessive fluid loss. The present invention addresses these needs with a drilling fluid that is “green” in the sense of benign with respect to its environmental effects.